This invention relates to an improved method and apparatus for grinding a tread edge or wing tip to remove material from, roughen, and shape its surface.
In the mounting of treads on a used tire casing, it is known in the art to buff the surface of the casing, removing the worn tread and roughening the remaining surface. This roughening of the casing improves the adhesion of a cushion layer of unvulcanized rubber which is cemented to the casing. The tread rubber is layered on and cemented to the cushion layer. This assembly is then cured. A similar procedure may be employed in applying a precured tread to a new tire cured casing. A new tire casing would be buffed in the crown region, without requiring the removal of the tread.
It has been determined that a roughening of a casing-contacting precured tread surface prior to cementing to the cushion layer improves the tread adhesion. The roughening procedure, commonly called buffing, is generally accomplished by the use of wire wheels. The wheels remove oxidized rubber and increase the surface area to be bonded, thus improving adhesion characteristics. Conventional buffing of the casing and the precured tread were directed circumferentially creating minute grooves around the circumferential surface of the tread and the casing.
With regard to winged treads, trials have shown that circumferentially buffing at the inner curvature of the wing did not produce a uniform buff. Uniformity of buffing being important to bond quality required that an alternative method be developed. Such a method was described in U.S. patent application Ser. No. 07/833,208.
It was the purpose of that invention to provide a method and apparatus for buffing a precured tread wherein the resulting roughened tread surface provided a means for improved air evacuation and an improved bond. This was accomplished by insuring that at least a portion of the roughened grooves terminated at the tread edges, thus providing a means for air evacuation.
It was a further purpose of that invention to describe and illustrate a method and apparatus for uniformly buffing a precured wing tread whereby the inner surfaces of the wings were uniformly roughened such that the grooves extended to a tread edge.
An improvement over the method described in U.S. patent application Ser. No. 07/833,208 has been discovered. A new method of grinding the inner and outer surfaces of the wing tip or edge of a precured tread can greatly reduce the potential of wing or edge lifting from the casing.